When you're writing an email, you can schedule it to be sent out at a later time. This can be handy if you're writing to someone in a different time zone, or if you just want to time an email to arrive at a more convenient time than when you're writing it.
One benefit of scheduling an email to send later is the ability to change your mind and cancel it.
Click the Scheduled category in the left pane.
All of the emails you have scheduled to send are shown.
Select the email you want to cancel.
Click the Cancel send button.
The scheduled send is cancelled, and the email is returned to your Drafts folder. From there, you can schedule it for another time, send it now, or delete it.